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1. Field of the Invention
The present invention relates to the placement of pipelines in a marine environment. More particularly, the present invention relates to an improved method and apparatus for laying a pipeline in a marine environment, wherein a specially configured pipeline laying ship provides a hull with a deck area and having a pair of reels independently rotatable during use, wherein a pipeline fabricating xe2x80x9cfiring linexe2x80x9d fabricates a pipeline that is then wound upon a selected one of the reels. The pipeline xe2x80x9cfiring linexe2x80x9d can be moved in order to align with either of the reels that is selected. Additionally, the pipeline can be payed out from either of the selected reels after it has been fabricated. A tower is provided for directing the pipeline from a reel through bend control and straightening stations and then to the seabed. The tower can be positioned at the vessel stern, or amidships for launching the pipeline through a vertical hull opening or xe2x80x9cmoon poolxe2x80x9d.
2. General Background of the Invention
For many years, pipelines have been fabricated at sea and lowered to the seabed at a desired location. For example, early patents to Tesson include U.S. Pat. Nos. 3,237,438 and 3,337,469 that are directed to a pipeline laying barge and method of operation. In the Tesson patents, the joints of pipe are welded on deck and then spooled or wound upon a reel. At a desired location, the pipeline is then placed on the seabed by unwinding the pipe from the reel and straightening it before it is lowered to the seabed.
A tilting tower has also been used to lower a pipeline to the seabed as the pipeline is being unwound from a reel. An example of such a titling tower and reel pipeline laying arrangement can be seen in the Uyeda U.S. Pat. No. 4,345,855 as an example. A similar arrangement is seen in the Springett U.S. Pat. No. 4,340,322. The Uyeda U.S. Pat. No. 4,345,855 and the Springett U.S Pat. No. 4,430,322 are hereby incorporated herein by reference. Another method of laying a pipeline is through the use of a stinger. A stinger is simply an elongated boom structure that extends from usually one end of a hull or barge. The stinger supports the pipeline as it is being lowered to the seabed. Examples of the use of stingers can be seen us U.S. Pat. Nos. RE28,922, RE29,591 and 5,533,834.
Reel type pipeline laying systems are typically employed in deep water situations. While it is known to weld the pipeline joints on the deck of a vessel and wind them upon a reel (for example, see the above discussed Tesson patents), it is also known to weld the pipeline on shore and then wind it upon the reel before the ship leaves port.
The following table provides an exemplary listing of patents that are known to applicant and that relate to pipeline laying vessels and methods of operation:
General Discussion of the Present Invention
The present invention provides an improved pipeline laying vessel and its method of operation. The method employs a preferably dynamically positioned barge or self-propelled dynamically positioned reel ship that has two independently rotatable reels or drums. The ship has a deck area that enables pipe joints to be welded together to form a pipeline. Joints of pipe are placed in a storage area on the deck of a vessel in suitable pipe racks. Welding stations near this storage area are arranged to receive multiple joints of pipe that have been internally cleaned and prepared for welding. Part of this preparation can include, for example, end bevels that are applied to the pipeline and to individual pipe joints.
As pipeline fabrication proceeds, pipe joints are moved from the rack storage areas to the pipeline fabrication area, also referred to herein as the xe2x80x9cfiring line.xe2x80x9d
This fabrication area or xe2x80x9cfiring linexe2x80x9d can comprise essentially a set of rollers supporting the pipeline along the center line of the fabrication area. Welding equipment (manual or automatic) can be provided together with known weld preparation tools.
The incoming pipe joints are aligned with the pipeline being fabricated. The welded area between the pipe joints and the joints previously welded together can be adjusted as required. The pipe joints are progressively welded together to form a pipeline at multiple welding stations. The welds are tested and field joints are then coated at another work station located in the pipeline fabrication area.
When one or more joints of pipe have been welded together end-to-end on the firing line, a selected reel or drum is readied for storage of the assembled pipeline on provided reels or drums. In keeping with the present invention, two (2) reels or drums are provided. A selected length (eg. about forty feet) of pipeline is advanced at any time and wound upon the reel by plastic bending. The pipeline moves ahead in the pipeline fabrication area by the same distance (eg. 40 feet increments) through a back tensioning device.
The pipeline welding progresses until the selected drum or reel is filled with the pipeline that is being welded on the deck of the vessel. Each reel or drum can be between 30 and 50 feet in diameter, have a width of between about 10-20 feet, and store, eg. 30,000-50,000 feet of six inch pipe.
In order to arrange properly the pipeline on the selected reel drum during spooling, the firing line travels from one side of the ship to the other side in a coordinated back and forth direction to spool each wrap of the pipeline next to the previous wrap on the reel.
The firing line can also be configured to travel from one side of the ship to the other side if it is to align with the second drum, so that the pipeline fabricated on the ship deck can be spooled on either one of the reels. In other words, the pipeline xe2x80x9cfiring linexe2x80x9d moves laterally as it is being spooled upon a first reel. However, the entire firing line can travel transversely on the ship""s deck a larger distance in order to align with the second reel when the second reel is to be filled with pipeline.
When the ship undertakes pipe laying on the sea bottom, the pipeline that is stored on a selected reel leaves the drum in a direction tracking toward the top of the tilting tower. The titling tower can tilt in a position that varies such as for example between about 65 and 95 degrees from the deck plane. At the top of the tower, the pipeline bends through a bend controller downwardly toward the seabed. The tilting tower can also be provided with a device for straightening the pipeline, a tensioning device and a clamping device that can hold the pipeline and support the weight of the pipeline that extends downwardly toward the seabed.
It should be understood that the general concept of paying a wound pipeline from a reel to a tilting tower that has a bend controller, straightener, tensioner, and clamp mechanism is old and known in the art such as is shown in the above discussed Springett U.S. Pat. No. 4,340,322 and Uyeda U.S. Pat. No. 4,345,855 patents, each incorporated herein by reference.
With the improved arrangement of the present invention, the tower can move transversely in a port to starboard direction and in a starboard to port direction for two reasons. The firing line can also be moved if necessary. The tower can move transversely in order to coordinate with the reel rotation. This arrangement enables spooling the welded pipeline upon the reel or removing pipeline from the reel in an orderly fashion. Secondly, the firing line and tilting tower can be moved transversely in order to align with either the first or the second drum as selected by the vessel operators. This larger transverse movement occurs when winding of the pipeline on the first reel is complete, and the winding of the pipeline on the second reel begins.
When leaving the bend controller, the pipeline passes through a straightening device that imposes a reversed plastic bending on the pipeline in order to straighten it. The straightened pipeline then passes through a vertical tensioner. The combined tension imposed on the pipeline by the tensioner and the drum back tension compensates for the suspended weight of the pipeline during its travel from the ship to the sea bottom. This tension is adjusted depending on the various pipe laying parameters such as pipeline characteristics (eg. diameter, wall thickness, coating, alloy, wet or dry lay) and water depth during lay operations. The proper tilting of the tower and the coordination of the tension with the ship as it moves along the pipeline route ensure that the stresses in the pipeline are maintained within predetermined predefined acceptable limits.
The area in between the last tensioner and the clamping mechanism or xe2x80x9chold offxe2x80x9d clamp can be used to support the pipeline and install corrosion anodes and insulation coating when required on the pipeline joints that are welded in the pipeline fabrication area or xe2x80x9cfiring line,xe2x80x9d or in the tower itself. A work station can be used to initiate the pipeline, lay down, and testing devices at the beginning and the end of the pipeline lay operations from either of the two reels.
The pipeline eventually leaves the ship after passing through the hold off clamp that has the ability to hold the pipeline suspended weight during lay down operations.
For pipelines that cannot be coiled on the reel drums, the tilting tower can be arranged to weld pipeline joints at one work station and to perform nondestructive testing and field joint coating at another work station.
The tension required to hold the weight of the suspended part of the pipeline being laid is being provided by the tensioner located on the tilting ramp and, when required, by the tension from an A and R (abandonment and recovery) winch wire. This wire can be routed to the top end of the pipeline through a sheave located on top of the tower. In this case, collars are welded to the linepipe and are used to transfer the A and R winch rope tension to the pipeline.
When an umbilical or flexible line installation is required, the ship can load this product in either a large capacity rotating basket located, for example, below deck, or on several smaller reels located on the ship deck, depending on the number of products, product length, and pipe characteristic, or on one or both of the main reels.
Such products can be laid on the sea bottom independently or simultaneously with the pipeline and attached as a xe2x80x9cpiggybackxe2x80x9d to the pipeline in the work station located in the tower. The product can be conveyed out of the storage areas to a position next and parallel to the pipeline in the tower by a second bend controller.
When a smaller diameter pipeline is to be laid (for example 2 inch-6 inch) with the main pipeline and as a piggyback to the main pipeline, this smaller pipeline is preferably fabricated on shore and stored on reels located on the ship""s deck. This smaller pipeline is conducted to the same position described above for umbilicals and flexible lines in the tower or work station. In this case, the small diameter pipeline is plastically bent and is straightened by another straightening device installed next to the one used for the main pipeline.
The present invention thus provides a method and apparatus for laying rigid pipelines, such as for example between 3 and 12 inches in diameter, on a sea bed and to lay, simultaneously or in sequence, long lengths of flexible products (umbilicals) and simultaneously limited lengths of small diameter (between about 2 inches and 6 inches) rigid pipelines. The system of the present invention thus provides a dynamically positioned ship of adequate length, width and depth.
The ship provides a deck that has multiple areas for storing pipeline lengths (linepipe or pipe joints). The deck provides an area for fabricating the pipeline from line pipe (firing line). A pair of storage reels are provided, preferably port and starboard reels. These reels or drums are powered separately from each other. Each drum or reel provides a back tension of, for example about 50 Te on the pipeline when it is used for pipe laying.
An area below deck can be provided to locate flexible products storage including for example a rotating basket.
An area on the deck is provided to locate multiple storage reels and their drives.
An opening on the deck is provided to load and unload flexible products into the below deck rotating basket.
An opening can be provided in the ship""s hull (moon pool) located, for example, approximately amidship.
A tilting tower is provided that preferably tilts between about 65 and 90 degrees from the deck plane.
A pipeline hold off clamp is located at the bottom end of the tilting tower. A retractable enclosure can be located at the middle part of the tilting tower to protect a provided work area.
Multiple pipeline tensioning devices can be provided, one located on the ship deck and one or two located vertically on the upper part of the tilting tower.
A device can be provided for straightening the pipeline during laying. A pipeline guiding device can be provided to conduct the pipeline from the reel that is used for pipe laying to the bend controller and straightener located on the tower.
A flexible product and small diameter rigid pipeline guiding device can be provided for conducting such products from their storage area on or below deck to the entry of the straightener.
Multiple work stations, such as welding stations can be provided on the tower.
A winch can be located below deck for lowering the pipeline to the sea floor when pipe laying is completed.
Multiple retractable sheaves can be used in conjunction with the winch.
The present invention thus provides an improved pipeline laying ship and its method of operation. The improved reel ship apparatus of the present invention includes a dynamically positioned barge or self-propelled dynamically positioned ship having a deck. A pair of reels or drums are supported upon the deck, each reel or drum being powered and independently rotatable. The reels are preferably positioned port and starboard relative to one another.
A pipe joint storage area is provided on the deck that contains multiple joints of pipe.
One or more pipeline welding stations on the deck define a xe2x80x9cfiring linexe2x80x9d that is positioned next to the reels. The pipeline welding stations are also positioned to join the joints of pipe together to form an elongated pipeline that can be wound upon a selected reel of said pair of reels.
After a selected reel has been filled with a pipeline, a tower is provided for guiding the elongated pipeline as it is unwound from the selected reel during the pipeline laying operation. The tower can include a bend controller, a straightener, a tensioner and a clamp mechanism.
The welding stations and tower are movably mounted upon the hull along a transverse path between port and starboard positions. This enables a pipeline to be welded and then wound upon either of the reels. Later, the pipeline can be unwound from either of the reels for launching to the sea bed via the tower.
The reels are preferably each supported to rotate about a generally horizontal axis.
The reels are preferably positioned generally parallel to one another and generally in between the pipeline welding stations on deck and the tower.
The present invention provides an improved method of laying a pipeline on a sea bed. The method first progressively joins joints of pipe (eg. 40 foot joints) together upon the deck of a vessel at a firing line to form a long pipeline. The vessel includes a pair of reels and a tower for launching the pipeline. The method includes winding the pipeline upon a selected reel of the pair of reels as the lengths pipe are joined (eg. welded) together at the firing line.
The method further includes the step of bending the pipeline to approximate the curvature of a reel before winding the pipeline upon the selected reel. With the present invention, one reel can be paying out a completed pipeline for placement on the seabed while the other reel is simultaneously being wound with a pipeline as it is being fabricated at the firing line. Two or more pipelines can be fabricated, reeled and then unwound for placement, and, if desired, joined together to make one very long pipeline.
After a selected reel is fully wound with a pipeline of selected length, the selected reel is moved along a path in which the pipeline is to be laid while unwinding the pipeline from the reel and simultaneously straightening the pipeline.
The method of the present invention provides that the reels are independently rotatable so that either reel can be wound with a pipeline independently of the other.
The method further includes the step of moving the firing line in a port to starboard direction that aligns the pipeline as it is being formed with a selected reel.
The method of the present invention also includes moving the tower in a port to starboard direction that aligns the tower with a selected reel during unwinding.
The reels preferably rotate about a generally horizontal axis and the method can further include the step of passing the straightened pipeline through a tensioner.
In the method of the present invention, the combined tension imposed on the pipeline by the tensioners and a drum back tension compensate for the suspended weight of the pipeline during its travel from the hull to the sea bed.
The method of the present invention further comprises the step of adjusting the tension on the pipeline depending upon pipeline laying parameters that include pipeline characteristics and water depth during pipe laying operation.
The method further includes providing a tower to guide the pipeline from a selected reel to the sea bed. The tower can be provided amidships for launching the pipeline through a vertical hull opening or xe2x80x9cmoon poolxe2x80x9d. The tower can be placed at the hull stern, behind the reels for launching the pipeline off the vessel stern. The method further comprises the step of coordinating the tension applied by the tensioner as the ship moves along the pipeline route to insure that the stresses in the pipeline are maintained with an acceptable limit.
The method of the present invention further includes the step of using a hold off clamp to support the pipeline so that corrosion anodes and insulation coating can be applied thereto. A moon pool can be provided for receiving the pipeline from the tower for launching to the seabed. Alternatively the tower can be positioned at the vessel stern for launching the pipeline off the stern.